the Thermo metric Anemometer. 695 



parameters. The asymptotes are given by v = and 

 W = 0-004147 vdd + hd0. The value v corresponding to the 

 minimum value o£ W is v = 242 \/ k. It is seen therefore 

 that if the experimental conditions are such that the relation 

 between the energy supply W and the velocity v is of the 

 hyperbolic type discussed, corresponding to very large values 

 of the velocity, the energy supply to maintain a difference of 

 temperature dO will be in excess of that represented by the 

 curve B by an amount hd6, and practically independent of k. 

 Moreover the thermometric type of anemometer would, under 

 the same conditions, permit the velocity to be uniquely deter- 

 mined from the energy supply, only if such velocity were, 

 in the case of the flow tube used in the present experiments, 

 known to be either le*s than or greater than 242 \/k. 

 Similarly in the general case, when the energy supply is 



given in the form W = $Qd0 + hdO + ~dd the minimum 



value of Q that can be uniquely determined from the value 



of the energy supply is equal to \f ^. The close approach 



to parallelism of the curve B and the various calibration 

 curves, more particularly those for small values of the 

 distance apart of the heating element and the second 

 thermometer, for large values of the impressed velocity of 

 the stream, indicates that the actual increase of temperature 

 of the stream was very approximately 2° C. Owing to the 

 increased facility for mixing occurring with slow flows, the 

 same was probably true in the case of low velocities of flow 

 also. 



The calibration curve A is approximately hyperbolic. It 

 will be noted however that for velocities of from 80 to 60 

 cms. per sec, the curve is slightly concave to the axis of 

 velocities. This sime feature of slight concavity is seen to 

 be present in all the other curves of the series. This charac- 

 teristic is probably attributable to the asymmetrical dispo- 

 sition of the resultant convection current from the heating- 

 element with regard to the two thermometers. Consider the 

 cane of curve A for which the two thermometers are disposed 

 at equal distances of 30 cm. from the heating element. 

 With zero flow, the two thermometers would indicate equal 

 temperatures, and the highest temperature in the flow 

 system would be found at the point immediately above the 

 heating element. When a slow flow is imposed, the region 

 of maximum temperature in the flow system is moved 

 towards the second thermometer. The energy requisite to 



